The present invention relates generally to solid catadioptric lens arrangement. More particularly the present invention relates to a solid catadioptric lens arrangement that incorporates a total internally reflective (TIR) collector portion that encompasses a light source to capture and collimate the light output and a projector lens portion that re-images the collimated light from the collector into the far field of the lens.
It is well known in the art that various combinations of lenses and reflectors can be used in conjunction to change the radiation distribution of the light emitted from a light source. For example, many flashlights available on the market today include a reflector cup around a light source to capture the radiation that is directed from the sides of the light source and redirect it in forward direction, and a convex lens that captures and focuses both the direct output from the light source and the redirected light from the reflector cup. While this is the common approach used in the manufacture of compact lighting devices such as flashlights, this method includes several inherent drawbacks. First, while this arrangement can capture much of the output radiation from the light source, the captured output is only slightly collimated. Light that exits from the light source directly without contacting the reflector surface still has a fairly a wide output angle that allows this direct light output to remain divergent in the far field of the lighting device. Therefore, to collimate this light in an acceptable manner and provide a focused beam, a strong refractive lens must be used. The drawback is that when a lens of this type is used, the image of the light source is directly transferred into the far field of the beam. Second, the light output is not well homogenized using an arrangement of this type. While providing facets on the interior of the reflector surface assists in smearing edges of the image, generally a perfect image of the actual light-generating source is transferred directly into the far field of the beam. In the case of an incandescent, halogen or xenon light source this is an image of a spirally wound filament and in the case of light emitting diodes (LEDs) it is a square image of the emitter die itself. Often this direct transfer of the light source image creates a rough appearance to the beam that is unattractive and distracting for the user of the light. Third, most of these configurations are inefficient and transfer only a small portion of the radiational output into the on axis output beam of the lighting device. Finally, these devices require several separate components to be assembled into mated relation. In this manner, these devices create additional manufacturing and assembly steps that increase the overall cost of the device and increase the chance of defects.
Several prior art catadioptric lenses combine the collector function with a refractive lens in a single device that captures and redirects the radiational output from a light source. U.S. Pat. No. 2,215,900, issued to Bitner, discloses a lens with a recess in the rear thereof into which the light source is placed. The angled sides of the lens act as reflective surfaces to capture light from the side of the light source and direct it in a forward mariner using TIR principals. The central portion of the lens is simply a convex element to capture the on axis illumination of the light source and re-image it into the far field. Further, U.S. Pat. No. 2,254,961, issued to Harris, discloses a similar arrangement as Bitner but discloses reflective metallic walls around the sides of the light source to capture lateral radiation. In both of these devices, the on-axis image of the light source is simply an image of the light generating element itself and the lateral radiation is transferred as a circle around the central image. In other words, there is little homogenizing of the light as it passes through the optical assembly. Further, since these devices anticipate the use of a point source type light element, such as is found in filament type lamps, a curvature is provided in the front of the cavity to capture the divergent on axis output emanating from a single point to create a collimated and parallel output. Therefore, a relatively shallow optical curvature is indicated in this application.
Another prior art catadioptric lens is shown in U.S. Pat. No. 5,757,557. This type collimator is referred to as the xe2x80x9cflat top tulipxe2x80x9d collimator. In its preferred embodiment, it is a solid plastic piece with an indentation at the entrance aperture. The wall of the indentation is a section of a circular cone and the indentation terminates in a shallow convex lens shape. A light source (in an appropriate package) injects its light into the entrance aperture indentation, and that light follows one of two general paths. On one path, it impinges on the inner (conic) wall of the solid collimator where it is refracted to the outer wall and subsequently reflected (typically by TIR) to the exit aperture. On the other path, it impinges on the refractive lens structure, and is then refracted towards the exit aperture. This is illustrated schematically in FIG. 1A. As stated above, the collimator 10 is designed to produce perfectly collimated light 16 from an ideal point source 12 placed at the focal point of the lens 10. A clear limitation is that when it is used with a real extended source 14 of appreciable surface area (such as an LED chip) as seen in FIG. 1B, the collimation is incomplete and the output is directed into a diverging conic beam that includes a clear image of the chip as a central high intensity region 18 and a secondary halo region 19.
There is therefore a need for a catadioptric lens assembly that collimates the light output from a light source while also homogenizing the output to produce a smoothly illuminated and uniform beam image in the far field of the device.
In this regard, the present invention provides an optical attachment for a light source. In particular, the present invention provides an optical element that is well suited for use with LED light sources, which do not approximate a point source for luminous flux output. The optical attachment includes a recessed area into which the light source is placed. The front of the recess further includes an inner lens area for gathering and focusing the portion of the beam output that is emitted by the light source along the optical axis of the optical attachment. Further, the optical attachment includes an outer reflector area for the portion of the source output that is directed laterally or at large angles relative to the optical axis of the device. The reflector portion and the inner lens direct the light output through a transition region where the light is focused and homogenized. The convex optics at the front of the transition region images this focused and homogenized light into the far field of the device. The present invention also relates to lens assembly as described above for use with other light sources such as incandescent, halogen or xenon, since these types of light sources are also well known in the art and are manufactured to be interchangeable with one another. The invention also relates to a flashlight device that includes a high intensity light source in conjunction with the optical lens described herein.
Accordingly, one of the objects of the present invention is the provision of compact one piece optical assembly that can be used with a high intensity light source to capture both the on axis and lateral luminous output and collimate the output to create a homogenous beam image in the far field of the device. Another object of the present invention is the provision of a one piece optical assembly for use with a high intensity light source that includes a TIR reflector assembly in conjunction with an on axis beam collimator at the input end thereof and a light tube that creates a focused and homogenous beam image for transfer into the far field of the device. A further object of the present invention is the provision of an optical assembly that creates a homogenous and focused beam image on the interior thereof that is further imaged into the far field of the output beam of the device to create a low angle beam divergence. Yet a further object of the present invention is the provision of a flashlight that includes a high intensity light source in combination with a one-piece optical assembly that creates a uniformly illuminated beam image in the far field of the device.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.